The degradation of an aromatic organic compound by Aspergillus niger var tubingensis Ed8 produces metabolites that reduce Cr (VI)

Chromium Cr(VI) is a highly toxic environmental contaminant for any organism, its presence in the environment is mainly due to anthropogenic activities. The use of biotechnology has been implemented for the treatment of effluents contaminated with Cr(VI).Our working group has isolated several fungi and bacteria capable of removing Cr(VI) from the culture medium. Aspergillus niger var tubingensis Ed8 is a strain that can produce metabolites which reduce Cr (VI) to Cr (III). The objective of this work was to determine the effect of sodium salicylate on the growth of this strain and on the Cr(VI) reduction system, as well as to identify the metabolites that are produced from sodium salicylate. Our results show that the Culture medium containing sodium salicylate (20 mM) inhibits strain growth compared to the control condition (0 mM). However, it increases the specific reduction capacity of Cr (VI) red/mg Biomass in order of magnitude. Analysis of the culture medium corresponding to 48 h of incubation shows the presence of catechol and salicylate diminution. In addition, as a product of the enzymatic activity of a cell-free cellular extract, after 24 h of incubation, the consumption of salicylate is detected, as well as the presence of peaks corresponding to resorcinol and catechol. Our results show that it is possible to increase the Cr(VI) reducing capacity of the Ed8 strain, depending on the composition of the culture medium.

Application of fungal copper carbonate nanoparticles as environmental catalysts: organic dye degradation and chromate removal

Biomineralization is a ubiquitous process in organisms to produce biominerals, and a wide range of metallic nanoscale minerals can be produced as a consequence of the interactions of micro-organisms with metals and minerals. Copper-bearing nanoparticles produced by biomineralization mechanisms have a variety of applications due to their remarkable catalytic efficiency, antibacterial properties and low production cost. In this study, we demonstrate the biotechnological potential of copper carbonate nanoparticles (CuNPs) synthesized using a carbonate-enriched biomass-free ureolytic fungal spent culture supernatant. The efficiency of the CuNPs in pollutant remediation was investigated using a dye (methyl red) and a toxic metal oxyanion, chromate Cr(VI). The biogenic CuNPs exhibited excellent catalytic properties in a Fenton-like reaction to degrade methyl red, and efficiently removed Cr(VI) from solution due to both adsorption and reduction of Cr(VI). X-ray photoelectron spectroscopy (XPS) identified the oxidation of reducing Cu species of the CuNPs during the reaction with Cr(VI). This work shows that urease-positive fungi can play an important role not only in the biorecovery of metals through the production of insoluble nanoscale carbonates, but also provides novel and simple strategies for the preparation of sustainable nanomineral products with catalytic properties applicable to the bioremediation of organic and metallic pollutants, solely and in mixtures.

Microbial reduction of metal-organic frameworks enables synergistic chromium removal

Redox interactions between electroactive bacteria and inorganic materials underpin many emerging technologies, but commonly used materials (e.g., metal oxides) suffer from limited tunability and can be challenging to characterize. In contrast, metal-organic frameworks exhibit well-defined structures, large surface areas, and extensive chemical tunability, but their utility as microbial substrates has not been examined. Here, we report that metal-organic frameworks can support the growth of the metal-respiring bacterium Shewanella oneidensis, specifically through the reduction of Fe(III). In a practical application, we show that cultures containing S. oneidensis and reduced metal-organic frameworks can remediate lethal concentrations of Cr(VI) over multiple cycles, and that pollutant removal exceeds the performance of either component in isolation or bio-reduced iron oxides. Our results demonstrate that frameworks can serve as growth substrates and suggest that they may offer an alternative to metal oxides in applications seeking to combine the advantages of bacterial metabolism and synthetic materials.

Interactions between electroactive bacteria and metal oxides are used for bioremediation. Here, the authors report on the application of Fe(III)-containing metal organic frameworks as substrates for bacterial growth which allow for remediation of lethal levels of chromium with high efficacy over several cycles.